This invention relates to a process for the preparation of polyisobutyl hydroxyaromatics. More particularly, this invention relates to a process for the preparation of polyisobutyl hydroxyaromatics which comprises alkylating a hydroxyaromatic compound with a polyisobutene having a methylvinylidene isomer content of at least about 70%.
Alkylation of hydroxyaromatic compounds with polymeric olefins using acidic catalysts to generate alkylphenols is well known in the art. However, use of the acidic catalysts required for the alkylation reaction gives rise to concurrent polymer degradation and fragmentation of the polymeric alkyl substituent on the hydroxyaromatic compound. Known acidic alkylation catalysts have various fragmenting effects depending on the size of the alkylating agent. Most catalysts have little effect on olefin alkylating agents of up to about 20 carbon atoms, that is, having a number average molecular weight of up to about 280, but severe fragmentation occurs where alkylating agents of higher molecular weights are used. Polymeric alkylating agents are usually derived from propylene or butene and those comprised primarily of polybutene are the most susceptible to fragmentation during the alkylation reaction. When polybutenes having a number average molecular weight of 300 or greater are used, molecular weight degradation of either the olefin polymer or the substituted alkyl group occurs.
British Patent No. 1,159,368 disclosed that fragmentation of both the alkylating agent and alkyl substituent can be reduced but not eliminated by the use of certain specified reaction conditions. These conditions include the use of boron trifluoride-phenolate as the acidic catalyst and a temperature range of 0.degree. C. to 65.degree. C., with 0.1 to 1.1 moles of boron trifluoride and 1 to 4 moles of phenol per mole of mono-olefinic polymeric alkylating agent having a molecular weight of 700 to 300,000. Under these conditions, the fragmentation of polybutene can still only be restricted at best to a level of about a 10% reduction of average molecular weight.
U.S. Pat. No. 4,238,628 to Cahill et al. discloses a process to reduce the molecular weight degradation during the alkylation of benzene, phenol and naphthol which comprises alkylating the aromatic compound in the presence of a boron trifluoride catalyst with a C.sub.3 or higher olefin polymer having terminal ethylene units.
According to the Cahill et al. process, the olefin polymer, preferably polybutene, is first reacted with ethylene to provide a polymer having terminal ethylene units. The polymer having such terminal ethylene units is then reacted with the aromatic compound under alkylating conditions. Cahill et al. teach that the olefin structure of the starting polybutene is predominantly the trisubstituted type with only minor amounts of vinylidene and terminal vinyl structures present.
Cahill et al. further teach that polyalkylphenols prepared with the use of polybutene without terminal ethylene units undergo molecular weight degradation due to the concurrent depolymerization reaction. Although the process disclosed in Cahill et al. results in a reduction in polymer degradation, the yield of the desired alkylaromatic product is not enhanced. In fact, the yield of alkylphenol reported by Cahill et al. ranged from about 44% to 64%.
Accordingly, there exists a need in the art for a hydroxyaromatic alkylation process which minimizes or eliminates molecular weight degradation while maintaining a high yield of the desired alkylaromatic product.